Re: ancestral apistos

[Mike & Diane Wise <apistowise@bewellnet.com>]

Bill,

>From what I understand about South American paleogeography, ocean invasions of the Amazon Basin occurred in the early Cenozoic Period, over 20 million years ago. Since then the basin has alternately been dry and a freshwater lake (or 2). At times the Amazon Basin is believed to have possibly had 2 outlets. One was eastward along the present day channel and the other (pre-Miocene Epoch) flowed into the Pacific. Once the Andes were welded onto the South American land mass (during the Miocene Epoch, over 5
million years ago) this western drainage was diverted into the proto-Orinoco River drainage until additional mountain build cut off it northern flow. Then it could only flow eastward. Most of my references are 20 years old. If you have some more recent ones, I would certainly like to hear of them.

I doubt that the genus Apistogramma separated from its progenitors any farther back than the Pliocene, no more than 4 million years ago. Like the species of the rift lakes of East Africa they have undergone rapid speciation. The shores of these great lakes - when they were present - helped early apistos to migrate circularly east and west around the present foothills of the Brazilian and Guiana Highlands.  There were also periods during the Pleistocene Epoch (2 million - 12,000 years bp) when the same basin
was dry savanna and the coast extended farther out into the Atlantic than it does now. This caused isolation of the species and new species arose from this isolation. The northward flow of the western Amazon rivers into the proto-Orinoco allowed the macmasteri-group to enter Colombian & Venezuela. Much of this is speculation, of course, so I'm always interested in hearing other peoples' opinions.

Mike Wise

William Vannerson wrote:

> >>There are at least 2 lineages of apistos that have invaded Guianan coastal streams.<<
>
> Tomas Hrbek spoke at one of our killie club meeting regarding the lineage of Rivulins in South America.  One of the interesting comments that is import to keep in mind is that the continent's geography has gone under massive changes over the millennia.  At one point, the oceans water levels rose so that the entire Amazon basin was part of a large saltwater sea.  The South American continent was basically two "island" land masses.  Then the waters receded and fresh water fish re-invaded the "new" rivers.
>
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